In cities across the country, charter schools have become known for anxiety-fueled lotteries, bitter disputes over sharing buildings with traditional schools and teaching methods that are sometimes unorthodox.

But in some states, charter schools have increasingly become associated with something more basic yet elusive: money.

In California _ a state besieged by budget cuts, where per-pupil spending is among the lowest in the nation _ dozens of schools converted to charters in the 1990s and 2000s in search of a funding boost.

Across the country, charter schools have access to hundreds of thousands of dollars in federal startup grants. In California, up until recently, charters were given the state's average per-pupil allotment; that meant schools in districts with below-average funding could receive additional money by chartering.

Moreover, a few years ago, the Los Angeles Unified School District increased the percentage of low-income students that schools needed to qualify for a federal aid program known as Title I, prompting another wave of schools to leave the traditional sector. As charters, they could keep access to the Title 1 funds even with lower percentages of low-income students.

Experts say many of these new charters haven't changed much about their day-to-day operations after making the switch: for instance, by making use of the autonomy over calendar and curriculum that charter schools are afforded. The experience in California has led some experts to question whether schools should be allowed to charter solely for financial gain.

"If a charter ... is just a way of infusing a school or a group of schools with additional resources, that's just a money grab," said Margaret Raymond, the director of Stanford University's Center for Research on Education Outcomes. "The charter movement doesn't accept that as a legitimate charter."

Most states allow traditional schools to convert to charters, but nowhere are conversions as numerous as in California. More than 220 schools in the state have switched over, according to the most recent data from the National Alliance for Public Charter Schools. About one-quarter of Los Angeles's 284 charter schools are conversions. Several California school districts with only one school have become "charter districts." In at least five California districts with multiple campuses, charters now compose nearly all the schools. Many of these "dependent" charters retain close ties to their districts.

With the change in the formula for statewide funding, though, some of the financial incentives for chartering have been removed and the trend is slowing, according to the California Charter Schools Association.

"We're seeing a precipitous decline," said Jed Wallace, the association's president and CEO.

When charter schools started in Minnesota more than 20 years ago, backers envisioned them as experimental alternatives to the traditional system. However, in a growing number of communities in California and elsewhere they no longer constitute a fringe alternative.

In some cases, the change is part of an effort to create a decentralized system with largely autonomous schools. But in other cases, including some California communities, charter proponents such as Stanford University's Raymond worry that when schools convert solely for the money it might muddle the definition of charters and ultimately weaken the movement. They've even taken to calling some of the conversions Chinos, for "charters in name only."

"There's a subset of these conversions that aren't charters, and we shouldn't think of them as charters," said Bryan Hassel, a co-director of Public Impact, an education reform group that works with policymakers, districts and charters. "It dilutes the concept, and so it makes it less clear what a charter school really is."

Nationally, conversion charter schools have grown from 422 in the 2009-10 school year to 591 in 2012-13. They now compose nearly 10 percent of all charter schools. Milwaukee Public Schools, for instance, has authorized 23 conversion charter schools. Half of Arkansas' 36 charters were once regular public schools. In Georgia, entire school districts are allowed to convert at once. So far, 17 have done so.

The Georgia Charter Schools Association, however, doesn't consider any of the conversion schools true charters under its definition, Executive Vice President Andrew Lewis said.

The California Charter Schools Association doesn't take so strong a stance. Wallace said he didn't view conversion schools as a "grave problem ... but it's certainly something we're watching closely."

(The Hechinger Report is a nonprofit education-news outlet based at Teachers College, Columbia University. This story was produced in partnership with The Center for Investigative Reporting.)